Total Population Predicted Class = False Predicted Class = True
Actual Class = False True Negative (TN) False Positive (FP)
Actual Class = True False Negative (FN) True Positive (TP)

 

So, in our example, the actual or expected output is:

Ya = [False, False, True, True, True, False, True, False, False, True]

And the predicted output is:

Y = [True, False, True, True, False, False, True, False, False, True]

So, the total number of:

True Negative = the output labels that are predicted to be False and they are actually False also = 4

False Positive = the output labels that are predicted to be True but they are actually False = 1

False Negative = output labels that are predicted to be False but they are actually True = 1

True Positive = output labels that are predicted to be True and they are actually True = 4

So, the confusion matrix will be like the following:

Total Population Predicted Class = False Predicted Class = True
Actual Class = False True Negative (TN) 4 False Positive (FP) 1
Actual Class = True False Negative (FN) 1 True Positive (TP) 4

 

How to calculate Confusion Matrix using the sklearn Python library?

We can use the following Python code to compute the confusion matrix.

from sklearn.metrics import confusion_matrix

Ya = [False, False, True, True, True, False, True, False, False, True]
Y = [True, False, True, True, False, False, True, False, False, True]

conf_matrix = confusion_matrix(Ya, Y)
print("Confusion Matrix: \n", conf_matrix)

Here, Ya is the actual or expected output and Y is the predicted output. The output of the above program will be:

Confusion Matrix: 
 [[4 1]
 [1 4]]
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Amrita Mitra

Author

Ms. Amrita Mitra is an author, who has authored the books “Cryptography And Public Key Infrastructure“, “Web Application Vulnerabilities And Prevention“, “A Guide To Cyber Security” and “Phishing: Detection, Analysis And Prevention“. She is also the founder of Asigosec Technologies, the company that owns The Security Buddy.

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